[PATCH RFC 0/4] Containerised NFS clients and teardown

[trondmy@kernel.org]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

When a NFS client is started from inside a container, it is often not
possible to ensure a safe shutdown and flush of the data before the
container orchestrator steps in to tear down the network. Typically,
what can happen is that the orchestrator triggers a lazy umount of the
mounted filesystems, then proceeds to delete virtual network device
links, bridges, NAT configurations, etc.

Once that happens, it may be impossible to reach into the container to
perform any further shutdown actions on the NFS client.

This patchset proposes to allow the client to deal with these situations
by treating the two errors ENETDOWN  and ENETUNREACH as being fatal.
The intention is to then allow the I/O queue to drain, and any remaining
RPC calls to error out, so that the lazy umounts can complete the
shutdown process.

In order to do so, a new mount option "fatal_errors" is introduced,
which can take the values "default", "none" and "enetdown:enetunreach".
The value "none" forces the existing behaviour, whereby hard mounts are
unaffected by the ENETDOWN and ENETUNREACH errors.
The value "enetdown:enetunreach" forces ENETDOWN and ENETUNREACH errors
to always be fatal.
If the user does not specify the "fatal_errors" option, or uses the
value "default", then ENETDOWN and ENETUNREACH will be fatal if the
mount was started from inside a network namespace that is not
"init_net", and otherwise not.

The expectation is that users will normally not need to set this option,
unless they are running inside a container, and want to prevent ENETDOWN
and ENETUNREACH from being fatal by setting "-ofatal_errors=none".

Trond Myklebust (4):
  NFS: Add a mount option to make ENETUNREACH errors fatal
  NFS: Treat ENETUNREACH errors as fatal in containers
  pNFS/flexfiles: Treat ENETUNREACH errors as fatal in containers
  pNFS/flexfiles: Report ENETDOWN as a connection error

 fs/nfs/client.c                        |  5 ++++
 fs/nfs/flexfilelayout/flexfilelayout.c | 24 ++++++++++++++--
 fs/nfs/fs_context.c                    | 38 ++++++++++++++++++++++++++
 fs/nfs/nfs3client.c                    |  2 ++
 fs/nfs/nfs4client.c                    |  5 ++++
 fs/nfs/nfs4proc.c                      |  3 ++
 fs/nfs/super.c                         |  2 ++
 include/linux/nfs4.h                   |  1 +
 include/linux/nfs_fs_sb.h              |  2 ++
 include/linux/sunrpc/clnt.h            |  5 +++-
 include/linux/sunrpc/sched.h           |  1 +
 net/sunrpc/clnt.c                      | 30 ++++++++++++++------
 12 files changed, 107 insertions(+), 11 deletions(-)

-- 
2.48.1